In the prior art, a fluorescent indicator to indicate a signal level to be measured in an acoustic instrument comprises a fluorescent indicating tube including a plurality of segment anodes arranged in parallel to each other in a row, a grid having a drive voltage applied thereto, and a filament having a voltage applied thereto, and a plurality of comparators having the number corresponding to that of the segment anodes and connected thereto, respectively. The comparators each have one input terminal to which a peak level or a detected output of an audio signal to be measured is applied, and have another input terminal to which reference voltages are applied. The reference voltages to the comparators are so different from each other that the reference voltages of the comparators sequentially or steppedly increase in their levels. Thus, the segments of the fluorescent indicating tube are ignited from the lowest level side toward the highest level side in accordance with the levels of the detected output to be measured. As the number of the segment anodes of the fluorescent indicating tube increases, the signal level can be indicated over a wide range of level and with more precision. With the prior fluorescent indicator, however, since there is required the number of the comparators or the driving circuits corresponding to that of the segment anodes of the fluorescent indicating tube, the size of the indicator tends to be larger while the cost of the indicator tends to be higher. This tendency is prominent in an acoustic instrument because the signal levels of left and right channels are to be normally indicated. Furthermore, the prior fluorescent indicator disadvantageously cannot indicate VU and peak levels in a simultaneous manner. The construction of the indicator will be more complicated in order to accomplish this.
In a tape recorder, if a magnetic head is not positioned in a proper vertical condition, the loss of a high frequency range is large and therefore an excellent characteristic of the tape recorder cannot be obtained. In order to accomplish a proper vertical condition of a magnetic head, in a prior tape recorder provided with a single reproducing head or a single recording/reproducing head, a test signal on a test tape for adjusting the vertical condition is reproduced by the reproducing or recording/reproducing head and read out by a vacuum tube volt meter (referred to as a VTVM hereinafter) while the magnetic head is adjusted in its vertical position so that the VTVM indicates the maximum output level, and in a prior tape recorder provided with both a recording head and a reproducing head separated from each other, a high frequency test signal on a magnetic tape recorded by the recording head is reproduced by the reproducing head and read out by a VTVM while the recording head is adjusted in its vertical position so that the VTVM indicates the maximum output level. However, various measuring devices such as a VTVM are required to adjust the magnetic head in its vertical position, and a high skill is also required to adjust the magnetic head so that the maximum output level is obtained at the VTVM.